Along with the development of miniaturized, light-weight and high performance electric devices, insulation systems have recently been required to be miniaturized and have high performance. One effective approach to meeting such requirements is to design a new shaped insulation system. However, conventional insulation sheets can be formed into only a limited variety of shapes due to their poor physical properties and poor formability.
Known conventional electric insulation sheets that can be used as an electric insulation sheet required to have Class F or higher heat resistance are, for example, a film made of a polyphenylene sulfide (hereinafter also referred to as PPS), a polyimide, and/or the like (see JP 55-35459 A), a laminated body composed of a wet-laid polyphenylene sulfide fiber nonwoven fabric and a synthetic resin film (see JP 63-237949 A), a laminated body composed of an unstretched polyphenylene sulfide sheet and a fiber sheet (see JP 8-197690 A), a laminated body composed of a fiber sheet and a silicone rubber (see JP 4-228696 A), and a paper composed of poly-m-phenyleneisophthalamide fibrids and poly-m-phenyleneisophthalamide fibers (see JP 2012-245728 A).
However, none of those conventional materials satisfies current requirements. For example, when the film of JP '459 is used alone, the surface is subject to scratching and, from the scratched part, cracking and tearing may occur. The film is poorly impregnated with a resin, and is difficult to fix to the peripheral components. The laminated body of JP '949 composed of the film and the fiber sheet is designed to prevent scratching on the film. The fiber sheet serves as a protective layer for the film, thereby solving the problems of cracking, tearing and poor resin impregnation. However, the design is not intended to exhibit adequate formability, and the laminated body thus has poor elongation, as a result of which the laminated body may tear during the formation process. JP '690 proposes a laminated body using an unstretched polyphenylene sulfide sheet to improve shock resistance and formability. In general, an unstretched polyphenylene sulfide sheet exhibits excellent formability when used alone. However, for a laminated body to exhibit excellent formability, all the materials that constitute the laminated body have to exhibit excellent formability. In JP '690, there is no limitation on the fiber sheet.
JP '696 proposes a laminated body composed of a fiber sheet and a silicone rubber. Since a silicone rubber is elastic, the laminated body has the advantage of less occurrence of overlapped wrinkles at the time of deep drawing. However, there still remains the problem of incapability of being formed into a shape that requires extensive elongation. JP '728 proposes a paper composed of poly-m-phenyleneisophthalamide fibrids and poly-m-phenyleneisophthalamide fibers. The paper cannot be softened or melted even under a high temperature of 200° C. or higher. Thus, the materials cannot be elongated during the forming process, and when the paper is excessively elongated, the paper will break.
As described above, a laminated body that has a good three-dimensional formability and results in low variability in the shapes of the products in a forming process and an excellent forming process yield has not been invented yet.
It could therefore be helpful to provide a laminated body that has a good three-dimensional formability and results in low variability in the shapes of the products in a forming process and an excellent forming process yield.